The role of TRPA1 and TRPV1 in the perception of astringency.

Astringency, commonly described as a drying, roughening, and/or puckering sensation associated with polyphenol-rich foods affects their palatability. While the compounds eliciting astringency are known, its mechanism of action is debated. This study investigated the role of transient receptor potential (TRP) channels A1 and V1 in astringency perception. If TRP A1 or V1 have a functional role in astringency perception, then desensitizing these receptors should decrease perceived astringency. Thirty-seven panelists underwent unilateral lingual desensitization of TRP A1 and V1 channels using mustard oil and capsaicin, respectively. Panelists then evaluated four astringent stimuli: epicatechin (EC), epigallocatechin gallate (EGCG), tannic acid (TA), and potassium alum (Alum), via 2-AFC and intensity ratings. When TRPA1 receptors were desensitized on one half of the tongue via mustard oil, no significant differences were observed between the treated and untreated sides for both 2-AFC and intensity ratings. Similarly, when TRPV1 receptors were desensitized on one half of the tongue via capsaicin, no significant differences were observed between the treated and untreated sides for both 2-AFC and intensity ratings. These findings challenge the notion that TRP channels play a pivotal role in astringency perception.

Astringency and its sub-qualities: a review of astringency mechanisms and methods for measuring saliva lubrication.

Astringency is an important mouthfeel attribute that influences the sensory experiences of many food and beverage products. While salivary lubricity loss and increased oral friction were previously believed to be the only astringency mechanisms, recent research has demonstrated that nontactile oral receptors can trigger astringency by responding to astringents without mechanical stimulation. Various human factors have also been identified that affect individual responses to astringents. This article presents a critical review of the key research milestones contributing to the current understanding of astringency mechanisms and the instrumental approaches used to quantify perceived astringency intensity. Although various chemical assays or physical measures mimic in-mouth processes involved in astringent mouthfeel, this review highlights how one chemical or physical approach can only provide a single measure of astringency determined by a specific mechanism. Subsequently, using a single measurement to predict astringency perception is overly idealistic. Astringency has not been quantified beyond the loss of saliva lubrication; therefore, nontactile receptor-based responses must also be explored. An important question remains about whether astringency is a single perception or involves distinct sub-qualities such as pucker, drying, and roughness. Although these sub-quality lexicons have been frequently cited, most studies currently view astringency as a single perception rather than dividing it into sub-qualities and investigating the potentially independent mechanisms of each. Addressing these knowledge gaps should be an important priority for future research.

Sensory Nutrition and Bitterness and Astringency of Polyphenols.

Recent studies have demonstrated that the interaction of dietary constituents with taste and olfactory receptors and nociceptors expressed in the oral cavity, nasal cavity and gastrointestinal tract regulate homeostasis through activation of the neuroendocrine system. Polyphenols, of which 8000 have been identified to date, represent the greatest diversity of secondary metabolites in plants, most of which are bitter and some of them astringent. Epidemiological studies have shown that polyphenol intake contributes to maintaining and improving cardiovascular, cognitive and sensory health. However, because polyphenols have very low bioavailability, the mechanisms of their beneficial effects are unknown. In this review, we focused on the taste of polyphenols from the perspective of sensory nutrition, summarized the results of previous studies on their relationship with bioregulation and discussed their future potential.

The perception and influencing factors of astringency, and health-promoting effects associated with phytochemicals: A comprehensive review.

Astringency as the complex sensory of drying or shrinking can be perceived from natural foods, including abundant phenolic compounds. Up to now, there have been two possible astringency perception mechanisms of phenolic compounds. The first possible mechanism involved chemosensors and mechanosensors and took salivary binding proteins as the premise. Although piecemeal reports about chemosensors, friction mechanosensor's perception mechanisms were absent. There might be another perception way because a part of astringent phenolic compounds also triggered astringency although they could not bind with salivary proteins, however, the specific mechanism was unclear. Structures caused the differences in astringency perception mechanisms and intensities. Except for structures, other influencing factors also changed astringency perception intensity and aimed to decrease it, which probably ignored the health-promoting effects of phenolic compounds. Therefore, we roundly summarized the chemosensor's perception processes of the first mechanism. Meanwhile, we speculated that friction mechanosensor's probably activated Piezo2 ion channel on cell membranes. Phenolic compounds directly binds with oral epithelial cells, activating Piezo2 ion channel probably the another astringency perception mechanism. Except for structure, the increase of pH values, ethanol concentrations, and viscosity not only lowered astringency perception but were beneficial to improve the bioaccessibility and bioavailability of astringent phenolic compounds, which contributed to stronger antioxidant, anti-inflammatory, antiaging and anticancer effects.

Mannoproteins, arabinogalactan protein, rhamnogalacturonan II and their pairwise combinations regulating wine astringency induced by the interaction of proanthocyanidins and proteins.

Roles of polysaccharides on modulating wine astringency from the perspective of polyphenol-proteins interaction has received increasing attention in last decade. In this work, proanthocyanidins extracts from three wines with different polyphenolic profiles and organoleptic properties were prepared to establish polyphenol-proteins interaction model wines. The effect of three wine polysaccharides including mannoproteins (MP), arabinogalactan protein (AGP) and rhamnogalacturonan II (RG-II) as well as their pairwise combinations on the interaction model wines were evaluated. Results showed that the structure and concentration of proanthocyanidins and polysaccharides had great influence on astringency. Proanthocyanidins with high mean degree of polymerization generated stronger astringency than others. Combining the results of fluorescence quenching and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, RG-II and other two polysaccharides (MP and AGP) modulated astringency through forming a ternary complex and competing reaction, respectively. Owing to synergetic effects, pairwise combinations of three polysaccharides (especially AGP + RG-II) reduced astringency more significantly than individual polysaccharides. Lower concentration (0.2 g/L-0.6 g/L) polysaccharides showed great contribution in modulating astringency. Sensory evaluation also verified the above-mentioned results. These findings were supposed to help better understand changes of astringency perception owing to the interaction of macromolecular substances in wine.

Astringency Sensitivity to Tannic Acid: Effect of Ageing and Saliva.

Astringency is an important sensory characteristic of food and beverages containing polyphenols. However, astringency perception in elderly people has not been previously documented. The aim of the present work was to evaluate sensitivity to astringency as a function of age, salivary flow and protein amount. Fifty-four panellists, including 30 elderly people (age = 75 ± 4.2 years) and 24 young people (age = 29.4 ± 3.8 years), participated in this study. Astringency sensitivity was evaluated by the 2-alternative forced choice (2-AFC) procedure using tannic acid solutions. Whole saliva was collected for 5 min before and after the sensory tests. The results showed that the astringency threshold was significantly higher in the elderly group than the young group. No correlation was observed between the salivary protein amount and threshold value. However, a negative correlation between salivary flow and threshold was observed in the young group only. These results showed a difference in oral astringency perception as a function of age. This difference can be linked to salivary properties that differ as a function of age.

Effects of epigallocatechin gallate, epigallocatechin and epicatechin gallate on the chemical and cell-based antioxidant activity, sensory properties, and cytotoxicity of a catechin-free model beverage.

The effects of epigallocatechin gallate (EGCG), epigallocatechin (EGC) and epicatechin gallate (ECG) on the chemical and cell-based antioxidant activity, sensory properties, and cytotoxicity of a catechin-free model beverage were modeled using response surface methodology. Results showed that ECG presented the highest reducing capacity while EGCG presented the highest Cu2+ chelating ability. Binary interactions (EGCG/EGC and EGCG/ECG) had an additive effect on CUPRAC, DPPH and Cu2+ chelating ability. The mixture containing 67.4% ECG and 32.6% EGCG was the optimal combination of flavanols (OPC). In a beverage model - chrysanthemum tea - OPC enhanced the anti-proliferative activity in relation to OVCAR-3, HEK293 and HFL1 cells and decreased the intracellular generation of reactive oxygen species. OPC enhanced the bitterness and astringency of the beverage models impacting in a decrease in overall acceptance. The pasteurization process did not decrease the antioxidant activity and the flavanol concentration of the beverages.

Cosmeceuticals: What's Real, What's Not.

Cosmeceuticals are cosmetics that promise to deliver physiologically relevant benefits without the incorporation of prescription drugs. To entice consumers to purchase these premium priced products, a story must be told of how the cosmeceutical delivers on these appearance improvement promises. The backbone of any cosmeceutical skin care regimen is facial cleansing and moisturizing. This article reviews the novel ingredients and technologies used to achieve these benefits examining what is real and what is not.

Impact of oral astringent stimuli on surface charge and morphology of the protein-rich pellicle at the tooth-saliva interphase.

The proteinaceous pellicle layer, which develops upon contact with saliva on the surface of teeth, is important for the formation of oral biofilms and for the protection of teeth from abrasion and chemically induced erosion. Astringent food ingredients comprising polyphenols, cationic macromolecules, and multivalent metal salts are known to interact with the pellicle. However, astringent-induced changes in the physicochemical properties of the tooth-saliva interphase are not yet completely understood. Here we provide comprehensive insights into interfacial charging, ultrastructure, thickness, and surface roughness of the pellicles formed on the model substrates silicon oxide (SiO2), Teflon® AF, and hydroxyapatite, as well as on bovine enamel before and after incubation with the astringents epigallocatechin gallate, tannic acid, iron(III) salt, lysozyme, and chitosan. Quartz crystal microbalance with dissipation monitoring demonstrated viscous behavior of untreated pellicles formed in vitro on the different materials. Electrokinetic (streaming current) measurements revealed that cationic astringents reverse the charge of native pellicles, whereas polyphenols did not change the charge under physiological pH condition. In addition, transmission electron microscopy and atomic force microscopy showed a concentration-dependent increase in average film thickness and pellicle surface roughness as induced by astringents. These multifaceted alterations of the salivary pellicle may come along with an increase in roughness perceived on the teeth, which is part of the complex sensations of oral astringency.

Effect of the addition of mannoproteins on the interaction between wine flavonols and salivary proteins.

It has been suggested that the addition of flavonols (i.e. white grape skins) improves and stabilizes the color of red wines. However, it has been shown that flavonol glycosides produce a mouth-drying and mouth-coating sensation at very low threshold concentrations. Moreover, the addition of polysaccharides to wines is a practice addressed to improve the smoothness and roundness and correct excessive astringency, so we have studied the effect of the addition of yeast mannoproteins (MP) on the interaction between quercetin 3-glucoside and human salivary peptides. Sensory analysis showed the first evidence of the mannoprotein smoothing effect when the flavonol is added to wine. Additionally, MP/SP/polyphenol interactions were studied using fluorescence spectroscopy, dynamic light scattering and isothermal titration calorimetry. Results obtained indicate not only the existence of interactions between mannoproteins and flavonols but also between mannoproteins and salivary proteins (SP), suggesting a possible formation of protein/polyphenol/polysaccharide ternary complex.

Evidence of traditionality of Brazilian medicinal plants: The case studies of Stryphnodendron adstringens (Mart.) Coville (barbatimão) barks and Copaifera spp. (copaíba) oleoresin in wound healing.

ETHNOPHARMACOLOGICAL RELEVANCE: The World Health Organization (WHO) recognizes the potential of plants used in secular traditional medicine and considers this an important source of evidence to assess their effectiveness and safety. Brazil is rich in biodiversity and traditional uses based on the Amerindian culture. However, many processes started with the arrival of the Portuguese in the year 1500. The successive economic cycles, for example, led to destruction of native vegetation and an intense cultural erosion. As a consequence, the information about the use of plants in the past centuries are dispersed and without interpretation. In this study a methodology to evidence the traditionality of Brazilian plants was demonstrated using data about barbatimão barks (Stryphnodendron adstringens (Mart.) Coville - Fabaceae) and Copaiba oleoresin (Copaifera spp. - Fabaceae) in wound healing, was established. MATERIAL AND METHODS: Data about use of the plants were recovered from bibliography published between 1576 and 2011. The books (101) were classified using weights, considering the date of publication and the source of Information. Older books that describe primary information received weight 10, while books written more recently and with secondary information received weight 0.4. A score for each category of medicinal use was calculated based on the books weights and the frequency of citation. A review about the current use of both plants was also performed from ethnobotanical studies published in journals. RESULTS AND DISCUSSION: The traditional secular use of barks of barbatimão and oleoresin of copaiba to treat wounds was confirmed based on the historic bibliographic research. The most frequent use of barbatimão in a timeline of 500 years of Brazil's history, was as astringent, whereas for copaíba was as healing of skin and mucosal lesions. The continuous and current use of these plants to treat wounds, confirmed by recent ethnobotanical studies, is an indicative of the resilience of these remedies and their effectiveness. CONCLUSION: The use of preparations containing barbatimão barks and copaiba oleoresin can be considered effective in the treatment of wounds. Nonetheless, it is necessary to improve the quality of the formulas as established by WHO.

Oral astringent stimuli alter the enamel pellicle's ultrastructure as revealed by electron microscopy.

OBJECTIVES: This electron microscopic study aimed at investigating effects of oral astringent stimuli on the enamel pellicle's morphology. METHODS: Pellicles were formed in situ within 30min on bovine enamel slabs, fixed to individuals' upper jaw splints. The pellicle-coated specimens were immersed in vitro in seven diverse astringent solutions and subsequently analyzed by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, as well as transmission electron microscopy (TEM). Four biocompatible astringents, namely the polyphenol epigallocatechin gallate, the metal salt iron(III) sulfate, the basic protein lysozyme, and the aminopolysaccharide chitosan, were additionally applied in situ. After rinsing the oral cavity with these compounds, the pellicle's ultrastructure was imaged by SEM and TEM, respectively. Untreated pellicle samples served as controls. RESULTS: Exposure to polyphenols and lysozyme induced particularly thicker and electron-denser pellicles in comparison to the control pellicle with similar characteristics in vitro and in situ. In contrast, acidic chitosan and metal salt solutions, respectively, revealed minor pellicle alterations. The incorporation of Fe and Al into the pellicles treated with the corresponding inorganic salts was verified by EDX analysis. CONCLUSIONS: Astringent-induced pellicle modifications were for the first time visualized by TEM. The ultrastructural alterations of the dental pellicle may partly explain the tooth-roughening effect caused by oral astringent stimuli. CLINICAL SIGNIFICANCE: Astringents might modify the pellicle's protective properties against dental erosion, attrition, as well as bacterial adhesion, and by this means may influence tooth health. The findings may thus be particularly relevant for preventive dentistry.

Sensory perception of and salivary protein response to astringency as a function of the 6-n-propylthioural (PROP) bitter-taste phenotype.

Individual differences in astringency perception are poorly understood. Astringency from tannins stimulates the release of specific classes of salivary proteins. These proteins form complexes with tannins, altering their perceived astringency and reducing their bioavailability. We studied the bitter compound, 6-n-propylthioural (PROP), as a phenotypic marker for variation in astringency perception and salivary protein responses. Seventy-nine subjects classified by PROP taster status rated cranberry juice cocktail (CJC; with added sugar) supplemented with 0, 1.5 or 2.0g/L tannic acid (TA). Saliva for protein analyses was collected at rest, or after stimulation with TA or cranberry juice (CJ; without added sugar). CJC with 1.5g/L tannic acid was found to be less astringent, and was liked more by PROP non-taster males than PROP taster males, consistent with the expectation that non-tasters are less sensitive to astringency. Levels of acidic Proline Rich Proteins (aPRPs) and basic Proline Rich Proteins (bPRPs) decreased after TA, while levels of aPRPs, bPRPs and Cystatins unexpectedly rose after CJ. Increases in bPRPs and Cystatins were only observed in PROP tasters. The PROP phenotype plays a gender-specific, but somewhat limited role in the perceived astringency of tannic-acid supplemented, cranberry juice cocktail. The PROP phenotype (regardless of gender) may also be involved in the release of salivary proteins previously implicated in oral health.

Inhibition of osteoblast differentiation by aluminum trichloride exposure is associated with inhibition of BMP-2/Smad pathway component expression.

Bone morphogenetic protein-2 (BMP-2)/Smad signaling pathway plays an important role in regulating osteoblast (OB) differentiation. OB differentiation is a key process of bone formation. Aluminum (Al) exposure inhibits bone formation and causes Al-induced bone disease. However, the mechanism is not fully understood. To investigate whether BMP-2/Smad signaling pathway is associated with OB differentiation in aluminum trichloride (AlCl3)-treated OBs, the primary rat OBs were cultured and exposed to 0 (control group, CG), 1/40 IC50 (low-dose group, LG), 1/20 IC50 (mid-dose group, MG), and 1/10 IC50 (high-dose group, HG) of AlCl3 for 24 h, respectively. We found that the expressions of OB differentiation markers (Runx-2, Osterix and ALP) and BMP-2/Smad signaling pathway components (BMP-2, BMPR-IA, p-BMPR-IA, BMPR-II, p-Smad1/5/8 and p-Smad1/5/8/4) were all decreased in AlCl3-treated OBs compared with the CG. These results indicated that inhibition of OB differentiation by AlCl3 was associated with inhibition of BMP-2/Smad pathway component expression. Our findings provide a novel insight into the mechanism of AlCl3-induced bone disease.

Investigating Mixture Interactions of Astringent Stimuli Using the Isobole Approach.

Astringents (alum, malic acid, tannic acid) representing 3 broad classes (multivalent salts, organic acids, and polyphenols) were characterized alone, and as 2- and 3-component mixtures using isoboles. In experiment 1, participants rated 7 attributes ("astringency," the sub-qualities "drying," "roughing," and "puckering," and the side tastes "bitterness," "sourness," and "sweetness") using direct scaling. Quality specific power functions were calculated for each stimulus. In experiment 2, the same participants characterized 2- and 3-component mixtures. Multiple factor analysis (MFA) and hierarchical clustering on attribute ratings across stimuli indicate "astringency" is highly related to "bitterness" as well as "puckering," and the subqualities "drying" and "roughing" are somewhat redundant. Moreover, power functions were used to calculate indices of interaction (I) for each attribute/mixture combination. For "astringency," there was evidence of antagonism, regardless of the type of mixture. Conversely, for subqualities, the pattern of interaction depended on the mixture type. Alum/tannic acid and tannic acid/malic acid mixtures showed evidence of synergy for "drying" and "roughing"; alum/malic acid mixtures showed evidence of antagonism for "drying," "roughing," and "puckering." Collectively, these data clarify some semantic ambiguity regarding astringency and its subqualities, as well as the nature of interactions of among different types of astringents. Present data are not inconsistent with the idea that astringency arises from multiple mechanisms, although it remains to be determined whether the synergy observed here might reflect simultaneous activation of these multiple mechanisms.

Minireview on Achillea millefolium Linn.

Yarrow (Achillea millefolium L.) is an important medicinal plant with different pharmaceutical uses. A. millefolium has been used for centuries to treat various diseases including malaria, hepatitis and jaundice. A. millefolium is commonly prescribed to treat liver disorders. It is also used as an anti-inflammatory agent and is a hepatoprotective herb. A. millefolium is considered safe for supplemental use. It has antihepatotoxic effects also. It is prescribed as an astringent agent. It is prescribed in hemorrhoids, headache, bleeding disorders, bruises, cough, influenza, pneumonia, kidney stones, high blood pressure, menstrual disorders, fever, rheumatoid arthritis, gout, osteoarthritis, hemorrhagic disorders, chicken pox, cystitis, diabetes mellitus, indigestion, dyspepsia, eczema, psoriasis and boils.

Effects of norepinephrine on immune functions of cultured splenic lymphocytes exposed to aluminum trichloride.

The aim of this study was to investigate the effect of norepinephrine (NE) on spleen lymphocytes exposed to aluminum trichloride (AlCl3). In this experiment, lymphocytes were isolated from spleens of healthy Wistar rats weighing about 130 g and cultured with RPMI-1640 medium containing the final concentration of 0.552 mmol/L AlCl3. NE was added to the cultured cells at the final concentrations of 0 (control group), 0.1 (low-dose group), 1 (mid-dose group), and 10 (high-dose group) nmol/L. No addition of both AlCl3 and NE serviced as blank (BG). The T lymphocyte proliferation; the contents of IL-2, TNF-α, and T lymphocyte subsets; immunoglobulin G (IgG) and intracellular cyclic adenosine monophosphate (cAMP) concentrations; and ß2-adrenergic receptor (ß2-AR) density were measured at the end of the culture. The result showed that NE decreased T lymphocyte proliferation and the contents of IL-2, TNF-α, and T lymphocyte subsets whereas increased the concentrations of IgG and intracellular cAMP and ß2-AR density of the lymphocyte exposed to AlCl3. AlCl3 exposure without adding NE showed the similar impacts on these measures compared with BG. The results suggested that NE aggravated AlCl3 immunotoxicity on the lymphocytes and disordered the immune functions of the lymphocyte through the ß2-AR-cAMP signal pathway.

Potential role of the binding of whey proteins to human buccal cells on the perception of astringency in whey protein beverages.

Whey protein beverages have been shown to be astringent, which means that they are not appealing to consumers. The exact mechanism of astringency in whey protein beverages is yet to be fully elucidated. In this preliminary study, the binding between ß-lactoglobulin (ß-LG), lactoferrin (LF) and human oral epithelial cells (HSC-2 and NO-1-N-1 cells) at pH 3.5 and pH 7.4 was assayed as a function of protein concentration using an enzyme-linked immunosorbent assay. The binding of ß-LG and LF to HSC-2 and NO-1-N-1 cells was dependent on protein type, protein concentration, pH and time. The intensity of the binding to HSC-2 and NO-1-N-1 cells was much greater for LF than for ß-LG and was protein concentration dependent, which was consistent with the in vivo astringency perception of LF and ß-LG. The findings demonstrated that the binding interaction between whey proteins and human oral epithelial cells may play an important role in the perception of astringency in whey protein beverages.

Precipitation of salivary proteins after the interaction with wine: the effect of ethanol, pH, fructose, and mannoproteins.

UNLABELLED: Astringency is a complex sensation mainly caused by the precipitation of salivary proteins with polyphenols. In wine it can be enhanced or reduced depending on the composition of the medium. In order to investigate the effect of ethanol, tartaric acid, fructose, and commercial mannoproteins (MPs) addition on the precipitation of salivary proteins, the saliva precipitation index (SPI) was determined by means of the sodium dodecyl sulphate polyacrylamide gel electrophoresis of human saliva after the reaction with Merlot wines and model solutions. Gelatin index, ethanol index, and Folin-Ciocalteu index were also determined. As resulted by Pearson's correlation, data on SPI were well correlated with the sensory analysis performed on the same samples. In a second experiment, increasing the ethanol (11%-13%-17%), MPs (0-2-8 g/L), fructose (0-2-6 g/L) level, and pH values (2.9-3.0-3.6), a decrease in the precipitation of salivary proteins was observed. A difference in the SPI between model solution and red wine stated that an influence of wine matrix on the precipitation of salivary proteins occurred. PRACTICAL APPLICATION: Results provide interesting suggestions for enologists, which could modulate the astringency of red wine by: (i) leaving some residual reducing sugars (such as fructose) in red wine during winemaking of grapes rich in tannins; (ii) avoiding the lowering of pH; (iii) adding commercial mannoproteins or promoting a "sur lie" aging; and (iv) harvesting grapes at high technological maturity in order to obtain wines with a satisfactory alcoholic content when possible.

Temporary modification of salivary protein profile and individual responses to repeated phenolic astringent stimuli.

The extent of the change in salivary protein characteristics after repeated stimulations was shown to be correlated to differences in perceived astringency. Salivary characteristics of 77 subjects were compared after masticatory (S1) and taste/masticatory (S2) stimulations. The variations (S2 minus S1) of protein concentration and saliva haze-forming capacity (HFC) were used to define 3 subject groups: low responding (LR, n = 20), medium responding (MR, n = 37), and high responding (HR, n = 20). Salivary protein concentration did not change in LR subjects; decreased a little, but significantly, in MR subjects; and strongly decreased in HR subjects. After S2, HFC increased in LR subjects, slightly decreased in MR subjects, and strongly decreased in HR subjects. Salivary protein electrophoresis patterns for HR and LR subjects were analyzed. No significant modifications of glycosylated proline-rich proteins (PRPs), PRPs, and amylases and a slight decrease in cystatins and histatins were found when S2 and S1 samples were compared in LR subjects, whereas HR subjects showed a strong decrease in all the above proteins after S2. Significant modifications of mucins were not found. Tannic acid (TA, 3 g/L) astringency ratings after S1 from HR subjects were significantly higher than those from the other 2 groups, whereas no differences were found comparing LR and MR ratings. The "carryover" effect due to 4 sequential exposures to TA samples (1.4 g/L) was observed in both HR and MR groups, whereas no significant astringency rating variation was found in the LR group. The results support the inhibiting role of proteins with strong phenol-binding activity on astringency elicitation. Individual physiological variations of parotid gland functionality might account for differences in sensitivity to astringent phenolic stimuli.